O2 Sensor Setting? or VE Table off?

[grantvoorhees]

Hello everyone. I am running a 454 BBC low compression motor. Power is around 225 hp at 3600 rpm and Torque is around 360 lbs./ft at 1600 rpm. I am running a 454 tbi unit on this engine with 2 81 lb/hr injectors. When I use the VE table generator it is dramatically different than what the autotune is correcting it for. One major problem that I am having is I am running a dual 2.25" exhaust, and the o2 sensor barely responds at idle or below 40 kPa manifold pressure. I know the autotune is getting closer to what it should be because the motor is smoothing out. I set idle the old fashioned way and added fuel until the motor stumbled and backed off fuel until it stumbled and found a happy medium. It did need 8 squirts of fuel for a smooth idle though, so the pwm pulse width is 1.6 ms at idle. It idles pretty smooth and the IAC is doing what it should, however it is just so far different from the ve table generator. Idle is around 550-600 rpm. Whether or not there is too little flow with the o2 sensor at low manifold pressure and rpm or what? I did notice that the engine does like to cruise around 20 kPa MAP on the street and freeway.

Is there a way to make the o2 sensor more effective on the lower end or should I tune by feel? It is wideband LC2.

[slow_hemi6]

At 8 squirts how is your DC at higher rpms? The table generator assumes that your required fuel value is spot on and more importantly that your dead time values and voltage correction are also spot on. Even then it is just an educated guess at best. At 8squirts you have 4 dead times per revolution so that value has to be fairly close to right or it effects the linearity of the expected values in the table.

[LT401Vette]

Check for exhaust leaks. Generally if the O2 doesn't read well at idle it is from a cam with a lot of over lap (doubtful here), or manifold / header leaks letting in air at low speeds.

[grantvoorhees]

Sorry I have been busy lately. The injector duty cycle is around 90% at about 3500 rpms, then drops down to around 80% as it runs out at WOT towards 4500-5000 rpm. This is probably because the heads flow great to about 3500 rpm and then fall flat on their face. I do have just a single wideband O2 sensor. I did weld in the bung around 18" downstream from the manifold, and at idle you can generally feel large pulses of airflow out the exhaust. There was an exhaust leak, but I welded that up last week. The motor doesn't have a cam and pulls 20 in Hg at idle and is smooth as can be. These heads are peanut port heads and are what they call high velocity heads. High flow in, high flow out. The dead time on the injectors are 1.0 ms and at 0.8 ms idle suffers.

I did try everything I could to get it to run on 4 squirts per cycle, but it feels like the cylinders are out of balance when I do, and no setting corrects this stumble besides running 8 pulses at idle. It does idle well at 550 rpm under load and 600 rpm with everything off. Each cylinder is just under 1 liter in displacement.

Would moving the o2 sensor further downstream help? Or are there O2 sensor settings that I can try and get a response?